The urbanization of America has resulted in a rapidly decreasing level of tolerance for offensive odors. Industries and municipalities have had to apply more and more sophisticated odor abatement treatment to avoid fines and orders to restrict operations based on complaints from the local community about nuisance odors.
Human wastes that were once simply deposited near the source dwelling are now carried away underground in a dilute aqueous stream from which the solids are removed by settling and the soluble nutrients are removed by biological action before the water is returned to the environment for re-use. In the recent past, the sludge remaining after primary and secondary treatment was disposed of by burial or by dumping at sea, but it must now be further treated to eliminate potentially hazardous organisms and odor.
Industries such as rendering, tanning, oil meal processing, manure drying, chemical manufacturing, paper manufacture, petroleum refining, especially those that involve both hydrophobic compounds and hot, humid gases, have odor problems that do not respond well to conventional odor abatement treatment.
Conventional odor abatement technology has been based on the premise that the main chemicals responsible for odor problems are either amines or sulfides. Amines are typically caught by scrubbing with sulfuric acid, while sulfides are typically caught by scrubbing with sodium hypochlorite. These processes have worked well enough often enough to become the predominant methods for odor abatement, but there have always been some difficult malodorous emissions for which conventional technology does not work consistently. [See "Odor Control", in "The Bio-Cycle Guide to Composting Municipal Wastes", The JG Press, Emmaus, PA, pages 35-43, 1989.]
In some cases, activated carbon can be used to adsorb difficult malodorous vapors from relatively dry gases, but it does not work well with gas streams above about 70% relative humidity. Activated carbon is expensive, and the spent adsorbent is not easily regenerated or disposed of.
As indicated above, conventional odor abatement processes attack the emitted odor directly. This is true in the cases of removing odorous amines and sulfides by scrubbing operations and difficult malodorous vapors by activated carbon. In many systems which emit malodorous components, including sewage treatment, not all emissions are of malodorous character. In fact, concentrations of relatively nonodorous organic compounds (many of which are condensible), are high compared with those of malodorous components. Conventional odor abatement treatments which attack the odor have largely ignored these organic compounds because they have inherently mild odors. The condensible components, however, are important to odor migration because they trap malodorous components on small droplets or particles, e.g., aerosol, which disperse into the atmosphere much less readily than gases.
Those skilled in the art have not recognized that relatively nonodorous components, e.g., from nominally inert bulking agents such as wood chips, sawdust, etc., may also make a significant contribution to odor problems. When emissions from such components are treated with conventional acid and bleach treatment the odor problem may become worse because some relatively nonodorous materials may be converted into compounds with undesirable odors.
It has been found that the above disadvantages can be overcome by an improved process whereby the known, but previously ignored, relatively nonodorous condensible organic components from odor-emitting operations, including sewage treatment plants, can be captured by being adsorbed to the surface of core particles. The process, by reducing or eliminating the condensation of so-called "sticky" oils onto aerosol of poor dispersibility to which normally dispersible malodorous materials, e.g., organic amines, sulfides, etc., become attached, results in materially reducing the concentration of malodorous components carried into the nearby community and provides a new perspective concerning odor abatement.